This project deals with the study of a genetic association between two functionally related loci in rats which operate in the vital process of oxygen transprot to tissues. The Dpg locus is the major locus responsible for variability in levels of 2,3-diphospho-glycerate (DPG) on outbred Long-Evans rats. DPG binds to hemoglobin (Hb) and lowers its affinity for oxygen (O2). This Dpg locus is genetically linked to a gene which determines Hb electrophoretic phenotype and is probably a Beta-globin gene (Hbb). Continued study of these rats will test the hypothesis the genotype at Dpg locus determines the specific activities of two key glycolytic control enzymes; phosphofructokinase (PFK) and pyruvate kinase (PK) by a mechanism which affects in vivo enzymes stability. Efforts will be made to pinpoint this mechanism. Kinetic and immunologic characterization of red cell PK from low and high-DPG animals will be completed. A strong linkage disequilibrium exists between the Dpg and Hbb loci which is of basic genetic interest. Characterization of developmental changes in expression of these loci may provide clues to a functional basis for this disequilibrium. Genotyping inbred rat lines at these loci will establish the frequency of association of alleles in the linkage phase found in the outbred population. The recombination frequency will be determined. Animals with low DPG levels, produce fewer ova and learn simple tasks more slowly than high-DPG animals. PFK and PK studies will increase our understanding of the nature of the Dpg locus so that we may answer the question of whether these differences in association traits are due to a mutant gene shared with red cells, a linked gene, or are due to DPG-related changes in Hb-O2 affinity. The role of Hb-O2 affinity in ovulation and cholesterol levels will be evaluated using exchange transfusion of high affinity blood. The long term goal of these experiments is to determine what the Dpg gene codes for and whether selection acts against recombinants at the Hbb and Dpg loci. The most important long term goal is to answer the question of whether low-DPG animals are at a disadvantage compared to high-DPG animals. Since a considerable range in DPG levels exists in normal human population, as well as many altered physiologic states, this project has obvious relevance to the human.